Fix missing semicolon in Book 2 listing 68

Resolves #1262

Author: armansito

books/RayTracingTheNextWeek.html

@@ -3676,7 +3676,7 @@
             p[2] = -sin_theta*rec.p[0] + cos_theta*rec.p[2];
 
             // Change the normal from object space to world space
-            auto normal = rec.normal
+            auto normal = rec.normal;
             normal[0] =  cos_theta*rec.normal[0] + sin_theta*rec.normal[2];
             normal[2] = -sin_theta*rec.normal[0] + cos_theta*rec.normal[2];